Which one of these are not a source of usable energy.

An object weighs 40n in air , weighs 20n when submerged jn water and 30n submerged in a liquid of unknown density .what is the density of the liquid?

The arrival of the conquistadors affected every indigenous people group they encountered. in this activity, you will write letters from the point of view of an incan and a conquistador. research the topic on the internet or at the library before writing. each letter should contain at least two paragraphs and be at least eight sentences long. 1) you are an inca and the conquistadors have arrived in your village! write a letter to be sent to other incan villages. describe your thoughts about the conquistadors and how their arrival might change your life. 2) write a letter from the point of view of a conquistador meeting the incas for the first time. address the letter to your family back in spain. me! i would really appreciate it! my dog died this morning and we are trying to fill out a form for her. it would amazing if you could me on this.

If both the president and the vice president can no longer serve, who will become the next head of state?